JP6930240B2 - Impact test evaluation method and impact tester - Google Patents

Description

The present invention relates to an impact test evaluation method and an impact tester for detecting a test force when a test piece is rapidly impacted with a force detector.

The impact test for evaluating the dynamic strength of a material is a tensile impact test (JISK7160 "Plastic-Tensile Impact Strength Test Method") that measures the energy when a test piece breaks due to a tensile impact at a specified speed. ), And a puncture impact test (JISK7211-2 "Plastic-hard plastic puncture impact test method") in which a striker is made to collide perpendicularly with the surface of the test piece to obtain an impact force-displacement diagram. When performing a tensile impact test with an impact tester, grip both ends of the test piece with the upper and lower grippers, drive the upper gripper at high speed with a hydraulic cylinder to pull the test piece, and use the load cell to apply the impact force when the test piece breaks. Detect (see Patent Document 1). Further, when performing a punching test such as a puncture impact test with an impact tester, the punch is collided with a test piece at high speed by a hydraulic cylinder to break it, and the collision test force at that time is detected by a detector (Patent Document). 2).

JP-A-2004-333221 JP-A-2004-333143

As described above, in a test in which a test jig such as an upper gripper or a punch is moved at high speed by a hydraulic cylinder to give an impact to the test piece, vibration or punch generated when the test piece breaks collides with the test piece. Occasional vibrations can spread throughout the testing machine. Further, in the impact test, noise due to the natural vibration of the impact tester is sometimes added to the test force waveform.

Knowing the natural frequency of the impact tester is important for knowing the exact test force value. As a method of obtaining the natural frequency of such an impact tester, for example, a test jig is connected to a force detector, and vibration waveform data generated by hitting the test jig with a hammer or the like is acquired. It is conceivable to perform frequency spectrum analysis of the waveform. However, when such a method is adopted, an accelerometer for collecting vibration waveform data, in addition to the usual test data collection performed by preparing a striking object such as a hammer and operating the testing machine, It is necessary to add an oscilloscope, data logger, etc. to the impact tester. Further, when adding such a device, in order to obtain accurate vibration waveform data, the user is required to correctly connect and operate each device, which causes a problem that preparation is complicated and time-consuming.

The present invention has been made to solve the above problems, and can easily and accurately obtain the natural frequency of the testing machine without adding a special device for measuring the natural frequency of the testing machine. It is an object of the present invention to provide an impact test evaluation method and an impact tester capable of reducing the influence of vibration derived from natural vibration.

The invention according to claim 1 is an evaluation method of an impact test in which a test piece is rapidly impacted, and the natural frequency of the testing machine is obtained from the time series data detected by the force detector by executing the impact test. A data extraction step for extracting a data section for the data, an analysis step for executing frequency spectrum analysis on the data extracted in the data extraction step, and a natural frequency and sampling determined from the frequency spectrum obtained in the analysis step. It includes a vibration waveform removing step of removing the natural vibration of the testing machine from the time series data using frequency.

The invention according to claim 2 is data determined by dividing the sampling frequency by a natural frequency determined from the frequency spectrum in the vibration waveform removing step in the impact test evaluation method according to claim 1. The moving average processing with points is executed for the time series data detected by the force detector.

The invention according to claim 3 is the method for evaluating an impact test according to claim 1, wherein in the vibration waveform removing step, the frequency that becomes the largest peak of the frequency spectrum is set as the natural frequency, and the sampling frequency is set as the sampling frequency. The moving averaging process at the data points determined by dividing by the natural frequency is executed on the time-series data detected by the force detector.

The invention according to claim 4 is an impact tester that rapidly impacts a test piece, a load mechanism that applies a test force to the test piece, and a force detection that detects a test force applied to the test piece. The control device includes a device and a control device provided with a storage unit that stores the time-series data detected by the force detector, and the control device comprises the natural vibration of the testing machine from the time-series data stored in the storage unit. A data extraction unit that extracts a data section for obtaining a number, an analysis unit that executes frequency spectrum analysis on the data extracted by the extraction unit, and a natural vibration determined from the frequency spectrum obtained by the analysis unit. It is provided with a vibration waveform removing unit that removes the natural vibration of the testing machine from the time series data by using the number and the sampling frequency.

According to the inventions of claims 1 to 4, it is possible to know the natural frequency of the testing machine from the test force data detected by the force detector when the impact test is executed. As described above, in the present invention, since it is not necessary to add a special device for measuring the natural frequency of the testing machine, it is not necessary to perform a complicated work of connecting the additional device, and the testing machine is operated by the additional device. It will not be expensive.

Further, according to the inventions of claims 1 to 4, since the natural vibration of the testing machine can be removed from the time series data detected by the testing machine by executing the impact test, the impact applied to the test force waveform. It is possible to know the accurate test force value from which the noise caused by the natural vibration of the testing machine has been removed.

It is a schematic diagram of the impact tester which concerns on this invention. It is a block diagram explaining the main control system of the impact tester which concerns on this invention. It is a flowchart which shows the measurement procedure of a natural vibration. It is a graph which shows an example of the time series data of a test force. It is a graph which shows the waveform before and after the fracture of the test piece TP in the graph of FIG. 4 in an enlarged manner. It is a flowchart which shows the analysis procedure of a natural frequency. It is a graph which shows an example of the time series data of a test force. It is a graph which shows the time series data after the test piece TP was broken. It is a graph which shows the frequency spectrum analysis result of the time series data shown in FIG. It is a flowchart which shows the procedure of removing a natural frequency from a time series data. It is a graph which shows the time series data before breaking of a test piece TP. It is a graph which shows the data which removed the natural frequency from the time series data of FIG.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of an impact tester according to the present invention. FIG. 2 is a block diagram illustrating a main control system of the impact tester according to the present invention.

This impact tester executes an impact test in which a test piece TP is rapidly impacted, and includes a tester main body 10 and a control device 40. The testing machine main body 10 includes a table 11, a pair of columns 12 erected on the table 11, a cross yoke 13 spanned by the pair of columns 12, and a hydraulic cylinder 31 fixed to the cross yoke 13.

The hydraulic cylinder 31 is operated by hydraulic oil supplied from a hydraulic source (not shown) arranged in the table via a servo valve 34. The upper gripper 21 is connected to the piston rod 32 of the hydraulic cylinder 31 via the approach jig 25 and the joint 26. On the other hand, the lower gripper 22 is connected to the table 11 via a load cell 27 which is a force detector. As described above, in the configuration of the testing machine main body 10, the approaching section is provided in the tensile direction by the approaching jig 25, and the piston rod 32 is pulled up at a high speed of 0.1 to 20 m / sec, thereby both ends of the test piece TP. It is configured to perform a tensile impact test in which a pair of gripping tools that grip a device are rapidly separated from each other. The displacement (stroke) of the load mechanism when the tensile impact test is executed, that is, the amount of movement of the piston rod 32 is detected by the stroke sensor 33, and the test force at that time is detected by the load cell 27.

The control device 40 includes a main body control device 41 for controlling the operation of the testing machine main body 10 and a personal computer 42. The main body control device 41 includes a memory 43 for storing a program, an arithmetic unit 45 such as an MPU (micro processing unit) for executing various operations, and a communication unit 46 for communicating with the personal computer 42. The memory 43, the arithmetic unit 45, and the communication unit 46 are connected to each other by a bus 61. Further, the main body control device 41 includes a test control unit 44 as a functional configuration. The test control unit 44 is stored in the memory 43 as a test control program. When the tensile impact test is executed, the control signal is supplied to the servo valve 34 and the hydraulic cylinder 31 operates by executing the test control program. The output signal of the stroke sensor 33 and the output signal of the load cell 27 are taken into the main body control device 41 at predetermined time intervals.

The personal computer 42 is a computing device such as a ROM for storing a data analysis program, a memory 51 including a RAM for loading a program and temporarily storing data when a program is executed, and a CPU (central processing unit) for executing various operations. It includes 55, a communication unit 56 that communicates with an externally connected device such as a main body control device 41, a storage device 57 that stores data, a display device 58, and an input device 59. The storage device 57 is a storage unit that stores time-series data of the test force of the impact test, and is composed of a large-capacity storage device such as an HDD (hard disk drive). The memory 51, the arithmetic unit 55, the communication unit 56, the storage device 57, the display device 58, and the input device 59 are connected to each other by a bus 71.

Further, as a functional configuration, the personal computer 42 is extracted by a data extraction unit 52 that extracts a data section for obtaining the natural frequency of the testing machine from the time series data of the test force in the analysis of the natural vibration described later. It includes an analysis unit 53 that executes frequency spectrum analysis on the data section, and a vibration waveform removal unit 54 that removes the natural vibration waveform of the testing machine from the test force data. The data extraction unit 52, the analysis unit 53, and the vibration waveform removal unit 54 are stored in the memory 51 as a data extraction program, an analysis program, and a vibration waveform removal program, respectively. These programs are executed by the action of the arithmetic unit 55.

The test force detected by the load cell 27 when the tensile impact test is executed is input to the memory 43 of the main body control device 41, and then transmitted from the communication unit 46 to the personal computer 42. The test force received by the communication unit 56 of the personal computer 42 is stored in the storage device 57 as time-series data.

FIG. 3 is a flowchart showing a measurement procedure of natural vibration. This flowchart shows the procedure for measuring the natural vibration in a tensile impact test using a synthetic resin piece such as PP (polypropylene), PC (polycarbonate), PS (polystyrene) as a test piece TP.

First, the upper gripping tool 21 and the lower gripping tool 22, which are jigs for the tensile impact test, are attached to the testing machine main body 10, and it is confirmed that the lower gripping tool is firmly fixed to the load cell 27. , Set the test conditions (step S11). The user sets test conditions such as test speed using the input device 59 of the personal computer 42. Then, both ends of the test piece TP are gripped by the upper gripping tool 21 and the lower gripping tool 22 (step S12).

Next, the data collection conditions are set (step S13). The user sets data collection conditions such as data collection start time-end time, sampling frequency, and number of acquired data points (sampling points) using the input device 59 of the personal computer 42. The natural vibration generated in the test machine main body 10 during the test can be obtained by observing the vibration that becomes remarkable when the load applied to the load cell 27 is removed by the breakage via the test piece TP. It is also necessary to know the test force in a state where the weight of the test jig (lower gripper 22 in this embodiment) is received without applying the test load. Therefore, in setting the data collection start time-end time, the number of data points (for example, the test piece TP) sufficient to acquire the data before the tensile load is applied to the test piece TP and to be used for the spectrum analysis described later is provided. It is preferable to set so that the number of data points after breaking is 1000 or more). In setting the sampling frequency and the number of sampling points, it is preferable to set a value at which the frequency resolution is 500 Hz or less by using the following equation (1).

Δf = 1 / T = Fs / N ... (1)
In the equation (1), Δf is the frequency resolution, T is the time window length, Fs is the sampling frequency, and N is the number of sampling points.

After setting the data collection conditions, the test is executed (step S14). The test force detected by the load cell 27 between the data collection start time and the end time set in the data collection conditions is sent to the personal computer 42 via the main body control device 41 and stored in the storage device 57, and the measurement ends. (Step S15).

FIG. 4 is a graph showing an example of time-series data of test force. FIG. 5 is an enlarged graph showing the waveform before and after the fracture of the test piece TP in the graph of FIG. In these graphs, the vertical axis is the test force (kN: kilonewton) and the horizontal axis is the time (μs: microseconds).

Whether or not the time-series data of the test force obtained by executing the test has a sufficient number of data points for spectrum analysis described later can be confirmed by using the equation (1). In the time-series data of the test force shown in the graph of FIG. 4, as shown enlarged in FIG. 5, the amplitude of the test force waveform becomes large at around 15,000 microseconds due to the breakage. As shown in FIG. 5, the starting point of the data after the breakage can be, for example, the time T1 in which the vibration waveform is one and a half cycles. If a sufficient number of data points cannot be obtained for spectrum analysis described later, the test piece TP is replaced (step S12), the data collection condition setting is changed (step S13), and the test is executed again. (Step 14).

FIG. 6 is a flowchart showing a procedure for analyzing the natural frequency. FIG. 7 is a graph showing an example of time-series data of test force. FIG. 8 is a graph showing time series data after the test piece TP is broken. In the graphs of FIGS. 7 and 8, the vertical axis represents the test force (kN: kilonewton) and the horizontal axis represents the time (μs: microseconds).

In the analysis of natural vibration, first, the time-series data of the test force acquired according to the measurement procedure shown in FIG. 3 is read from the storage device 57, and the time-series data is separated before and after the test force is removed from the test piece TP (step). S21). The graph shown in FIG. 7 is test force data obtained by executing a tensile impact test at a test speed of 5 m / s and acquiring a sampling frequency of 1000 kHz. In the tensile impact test, the time series data is separated before and after the fracture of the test piece TP. In the separation of the time series data of the test force, as described with reference to FIG. 5, the time T1 is set, and the data is separated before and after the time T1. Then, as shown by the broken line in FIG. 7, the data after the time T1 (2440 microseconds) is extracted as a data section for obtaining the natural frequency of the testing machine (step S22: data extraction step). After that, the frequency spectrum analysis by FFT (Fast Fourier Transform: Fast Fourier Transform) is executed on the time series data after the test piece TP shown in FIG. 8 extracted in step S22 is broken (step S23: analysis step). ).

FIG. 9 is a graph showing the frequency spectrum analysis result of the time series data shown in FIG. In this graph, the horizontal axis represents frequency (Hz: Hertz), and the vertical axis represents power for each frequency resolution Δf.

The result of the frequency spectrum analysis is displayed on the display device 58 and stored in the storage device 57. In the power spectrum shown in FIG. 9, the frequency with the largest peak is set to 13.8 kHz as the natural frequency (step S24).

FIG. 10 is a flowchart showing a procedure for removing the natural frequency from the time series data. FIG. 11 is a graph showing time-series data before breaking of the test piece TP, and FIG. 12 is a graph showing data obtained by removing the natural frequency from the time-series data of FIG. In these graphs, the vertical axis is the test force (kN: kilonewton) and the horizontal axis is the time (μs: microseconds).

If the natural frequency of the testing machine main body 10 is known, the accurate test force during the tensile impact test can be known by removing the natural vibration using the natural frequency from the time series data acquired by executing the test. .. First, a data range for removing the natural vibration waveform is selected (step S31), and the natural vibration of the testing machine considered to be superimposed on the data is removed from the time series data by using the moving average processing (step S32:). Vibration waveform removal process).

In this embodiment, as shown in FIG. 11, in the natural frequency analysis procedure, the test piece TP is subjected to a tensile load among the data obtained by separating the time series data of FIG. 7 before and after the breakage of the test piece TP. The time-series data before breaking of the test piece TP including the time data of the state is called from the storage device 57 with the natural frequency as the data to be removed. Even if the natural vibration of the testing machine does not seem to be superimposed on the data at first glance, if you want to remove the natural vibration of the testing machine body 10 from the entire time series data before separation, data separation You can select the previous time series data.

In step S32, the number of data points used for the moving average processing is determined by the following equation (2) using the natural frequency determined in step S24 described above and the sampling frequency at the time of data acquisition.

Number of data points = sampling frequency / natural frequency ... (2)

The data in FIG. 11 was obtained by performing a tensile impact test under the condition of a test speed of 5 m / s and at a sampling frequency of 1000 kHz. Therefore, the integer portion of 72.4 obtained by dividing the sampling frequency of 1000 kHz by the natural frequency of 13.8 kHz obtained in step S24 is the data score. If the value obtained by dividing the sampling frequency by the natural frequency integer does not become an integer as in this example, the value after the decimal point is rounded off or rounded off to obtain an integer value.

In the moving average processing, the data to be averaged is averaged using the same number of data before and after (including the case where the score is different by 1 before and after). In the data of FIG. 11, since the number of data points used for the moving average processing was set to 72 points in the calculation using the equation (2), the front 35 points centered on the data to be averaged (36th point). , The averaging process is executed with 36 points behind. When the moving average processing for the time-series data selected as the processing target is completed, the removal of the natural vibration is completed (step S33). The data after the moving average processing is displayed on the display device 58 in a manner in which the data before the processing and the data after the processing can be compared.

Comparing the data obtained by removing the natural vibration waveform by the moving average processing shown in FIG. 12 and the data before the moving average processing shown in FIG. 11, the data shown in FIG. 12 shows smoother behavior and the tensile load is higher. It is understood that the natural vibration of the testing machine affects the measured value of the load cell 27 even in the state of being applied to the test piece TP. In the example shown in FIG. 12, in the frequency spectrum analysis described with reference to FIG. 9, the maximum peak of 13.8 kHz was set as the natural frequency and the moving average processing was performed, but some peaks were set to the natural frequency. As candidates for, moving average processing may be performed on those candidates.

As described above, in the present invention, since the evaluation method in consideration of the natural frequency of the testing machine is adopted for the evaluation of the impact test, the waveform from which the noise due to the natural vibration of the testing machine is removed can be obtained. It is possible to know the accurate test force value. Further, in the present invention, since the data before and after the removal of the natural vibration waveform can be viewed on the same time axis, the user can see the influence of the natural vibration of the tester on the test force data in each impact test. You can check.

In the above-described embodiment, the tensile impact test has been described, but it is also possible to perform an impact test in which the punch is dropped onto a test piece supported by a fulcrum, such as a punching test in which the punch collides with a test piece and a three-point bending test. , The present invention can be applied.

10 Testing machine body 11 Table 12 Strut 13 Cross yoke 21 Upper gripper 22 Lower gripper 25 Assistance jig 26 Joint 27 Load cell 31 Hydraulic cylinder 32 Piston rod 33 Stroke sensor 34 Servo valve 40 Control device 41 Main body control device 42 Personal computer 43 Memory 44 Test control unit 45 Arithmetic unit 46 Communication unit 51 Memory 52 Data extraction unit 53 Analysis unit 54 Vibration waveform removal unit 55 Arithmetic unit 56 Communication unit 57 Storage device 58 Display device 59 Input device TP test piece

Claims (4)

It is an evaluation method of an impact test that gives a rapid impact to a test piece.
The data collection condition setting process in which the user sets the data collection conditions including the sampling frequency, and
Data extraction step to extract data after the test piece breaks as a data section for obtaining the natural frequency of the testing machine from the time series data acquired by the force detector under the data collection conditions by executing the impact test. When,
An analysis step of obtaining the natural frequency by executing frequency spectrum analysis on the data extracted in the data extraction step, and
Using said sampling frequency before and SL-specific frequency, the vibration waveform removal step of removing the natural frequency of the tester from the time-series data,
Impact test evaluation method including. In the impact test evaluation method according to claim 1,
The vibration waveform removal step, executes a moving average process in the defined data points by dividing the sampling frequency by the natural frequency determined from the frequency spectrum with respect to the time series data detected by the force detector How to evaluate the impact test. In the impact test evaluation method according to claim 1,
The vibration waveform removal step, the frequency of the largest peak of the frequency spectrum and the natural frequency, said force detecting a moving average process of the sampling frequency data points that defines by dividing the natural frequency An impact test evaluation method performed on the time-series data detected by the instrument. It is an impact tester that rapidly impacts the test piece.
A load mechanism that gives test force to the test piece,
A force detector that detects the test force applied to the test piece, and
A control device provided with a storage unit that stores time-series data detected by the force detector, and
With
The control device is
An input device that accepts user settings for data collection conditions, including sampling frequency,
A data extraction unit that extracts data after the test piece is broken as a data section for obtaining the natural frequency of the testing machine from the time series data stored in the storage unit and acquired under the data collection conditions. ,
An analysis unit that obtains the natural frequency by executing frequency spectrum analysis on the data extracted by the extraction unit.
Before SL using unique frequency and said sampling frequency, the vibration waveform removal unit for removing the natural frequency of the tester from the time-series data,
Impact tester equipped with.

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